Check if I'm in a shell through ranger

In ranger, you can hit S to jump into a shell and ctrl+D to get back to ranger. When I've been in a shell for a while and I want to jump to ranger, I'm unsure if this is a regular shell and I should hit ranger or if I'm in the shell through ranger already and I should hit ctrl+D. If I hit ctrl+D wrongly, my terminal will close. If I use ranger wrongly, I'll get a nested instance of ranger within ranger. Is there a way to check if I'm already in a ranger shell? If there is a command, I could alias it to something like rangerp which will output "True" if I am in a shell and "False" if I'm not.